Posted: 3/26/16 at 7:12am
Yes, I think those entire sections are supposed to be darkly humorous. The only parts of the novel that aren't a black comedy, and completely omitted from the film, are the detailed torture and murder scenes. Some of it is rather stomach churning and disgusting to get through.
I guess I will put up a slight spoilers tag to discuss the murders**********
The ending is a little ambiguous, but I believe zero murders have actually been committed. Patrick is a shell of a human being- I think he has a monologue where he says he has the outward appearance of a human, but the only two emotions he is capable of feeling are greed and disgust. His materialistic obsessions have consumed him and hollowed him out. I think he is so bored with life and his friends that he imagines these horrible murders as the only way he can feel alive and experience exhilaration, joy, etc.
He applies the same detailed descriptions of clothes and food to what he would do to all his victims. His delusions start to spin into total madness. In the film they make this section pretty clear when the ATM tells him to feed it the kitten and he shoots the security guard only walk back through the revolving door to find him still alive. The helicopter chase ensues and he leaves that voicemail for his lawyer. (In the novel a park bench gets up and starts chasing him!)
Patrick goes to Paul's apartment expecting to find rotting bodies, but instead a realtor is showing the place to a couple. The kicker is of course the conversation with the lawyer where he thinks Patrick was making a big joke. He tells Patrick that he dined with Paul not once but twice in London over the past 10 days. (Of course everyone is misidentified so often in the book that you could argue the lawyer had been eating with someone else he mistook for Paul, but that was not my takeaway at this point in the story.)